The photograph shows a hooded young man looking toward the sky just after he apparently threw something. Close by, a Citroen compact car is completely engulfed in flames.

The image is one of thousands of terrifying photos circulating in printed media and online outlets such as Facebook and Twitter following three nights of some of the most intense rioting in London in 30 years. The riots started on Sunday night following a peaceful march protesting the fatal shooting of a 29-year-old man by police.

Cars burn on a street in Ealing, London. (Toby Melville / Reuters)

The photo has been posted on the Tumbler blogging platform on a page called "Catch a Looter," a grassroots attempt to help police identify some of the more flagrant participants in the riots who have set buses on fire, looted shops and clashed with police.

"Catch a Looter" is also posting videos, including the horrific one of a young boy sitting on the ground bleeding. He is helped up by one man, who pretends to aid him while another opens and then surreptitiously steals items from the boy's backpack. Blood stains the sidewalk as he stumbles away.

The site's creator, who did not want to be identified, said he wanted "to do something to help fight back against the opportunistic thieves and thugs who are ruining people's lives casually and entirely for their own benefit."

"My intention isn't to start a witch hunt or vigilante group, merely to gather all the photos in one place for ease of use," he said.

U.K. police and government officials have stressed that in the coming days they will seek to identify and prosecute people believed to have taken part in the city-wide rampages. Social networking and media sites will play an important role.

"We have been making arrests all evening and have a team working during the night examining CCTV images," according to a statement on Tuesday from the MPS.

The efforts are a more positive spin on the use of technology amid the disturbances. As with any major news event, Twitter is filled with posts, many labeled with the hashtag "#londonriots."

Ben Firshman, the co-founder of a company that supports hosting for applications written in Python, built an application that plots tweets with the #londonriots hashtag and places them on a Google map.

"Sony warehouse still belching out smoke and visible from E3," wrote one user whose tweet was plotted on Monday evening. Sony's main optical disc distribution warehouse for the U.K. was hit by a large fire, although it was unclear on Tuesday if the cause was linked to the riots.

Some hoodlums were also apparently using Twitter to rally rioters to certain locations. But one of the top trending topics on Twitter on Tuesday was more positive: a hashtag "#riotcleanup," with posts detailing how people can get involved in cleaning up some of the hardest hit neighborhoods. A website listing cleanup activities is also online.

Facebook has also been a factor. On Tuesday, police in Glasgow said they detained a 16-year-old boy with posting a message on the social networking site "inciting others to commit acts of disorder."

"This detention shows that we are monitoring the situation closely," Strathclyde Police said in a statement.

The riots have been not been great publicity for Research in Motion, maker of the BlackBerry devices. Numerous news stories said teenagers were using RIM's Blackberry Messenger application to arrange disturbances across the city.

RIM estimates there are some 7 million or so users of BlackBerry devices. While mostly associated with corporate users, the devices are popular with youth in the U.K. for its BlackBerry Messenger application, which is free and is used instead of sending SMS (short message service).

The service is encrypted and not public, raising questions of whether the U.K. authorities will ask for assistance from RIM in their investigations.

"We have engaged with the authorities to assist in any way we can," said Patrick Spence, managing director, global sales and regional marketing at RIM, in an e-mail statement. "As in all markets around the world where BlackBerry is available, we cooperate with local telecommunications operators, law enforcement and regulatory officials."